时钟不开始

Question

我在JavaFX8中写了一个小时钟。在我的家伙，我有2个按钮。一个按钮应启动计时器，另一个按钮应暂停计时器。但每当我按下开始时，什么都没发生。当我删除整个if（）子句时，我能够通过thread.start启动计时器并更新我的gui。我认为我的电话“if（isRunning）”并不是我想要的......：P 我感谢任何帮助！

My Window.java（主要应用程序）

    /*
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 * and open the template in the editor.
 */
package gui;

import java.util.Observable;
import java.util.Observer;
import javafx.application.Application;
import javafx.application.Platform;
import javafx.event.ActionEvent;
import javafx.geometry.Insets;
import javafx.geometry.Pos;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.control.Label;
import javafx.scene.layout.BorderPane;
import javafx.scene.layout.HBox;
import javafx.stage.Stage;
import logic.Clock;
import logic.ClockObserver;

/**
 *
 * @author 
 */
public class Window extends Application implements Observer {

    private Button b_start = new Button("Start");
    private Button b_stop = new Button("Stop");
    private Label l_time = new Label("gdfgdf");
    private HBox buttonbox = new HBox();
    private Clock clock = new Clock();
    private Thread thread = new Thread(clock);

    @Override
    public void start(Stage primaryStage) throws Exception {
        thread.start();
        buttonbox.setSpacing(5.0);
        clock.addObserver(this);
        buttonbox.setAlignment(Pos.CENTER);
        buttonbox.getChildren().addAll(b_start, b_stop);
        BorderPane bp = new BorderPane();
        bp.setPadding(new Insets(10.0));
        bp.setCenter(l_time);
        bp.setBottom(buttonbox);
        Scene scene = new Scene(bp);
        primaryStage.setMinHeight(150);
        primaryStage.setMinWidth(250);
        primaryStage.setScene(scene);
        primaryStage.setTitle("Uhr");
        primaryStage.show();

        b_start.setOnAction((ActionEvent e) ->{
            clock.setRunning(true);
        });

        b_stop.setOnAction((ActionEvent e) ->{
            clock.setRunning(false);
        });
    }

    public static void main(String args[]) {
        launch(args);
    }

    @Override
    public void update(Observable o, Object o1) {
        Platform.runLater(new Runnable(){
            @Override
            public void run() {
                l_time.setText(clock.getZeit());
            }

        });
    }


}

我的Clock.java

    /*
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 * To change this template file, choose Tools | Templates
 * and open the template in the editor.
 */
package logic;

import gui.Window;
import java.util.Observable;
import java.util.logging.Level;
import java.util.logging.Logger;
import javafx.application.Platform;

/**
 *
 * @author
 */
public class Clock extends Observable implements Runnable {

    private String zeit = "";
    private int sek;
    private boolean isRunning = false;

    public Clock() {

    }

    public void setZeit() {
        zeit = "" + sek;
    }

    public String getZeit() {
        return zeit;
    }

    public void setRunning(boolean running){
        this.isRunning = running;
    }

    public boolean isRunning(){
        return isRunning;
    }

    public int getSek() {
        return sek;
    }

    @Override
    public void run() {
        while (true) {
            if (isRunning()) {
                try {
                    sek++;
                    setZeit();
                    System.out.println(zeit);
                    this.setChanged();
                    this.notifyObservers();
                    Thread.sleep(1000);
                } catch (InterruptedException ex) {
                    //TODO
                }
            }
        }
    }
}

提前致谢！